C3 molecules internalize and enhance the growth of Lewis lung carcinoma cells

The versatile functions of complement C3-derived ligands

The complement system is a major component of immune defense. Activation of the complement cascade by foreign substances and altered self-structures may lead to the elimination of the activating agent, and during the enzymatic cascade, several biologically active fragments are generated. Most immune regulatory effects of complement are mediated by the activation products of C3, the central component. The indispensable role of C3 in opsonic phagocytosis as well as in the regulation of humoral immune response is known for long, while the involvement of complement in T-cell biology have been revealed in the past few years. In this review, we discuss the immune modulatory functions of C3-derived fragments focusing on their role in processes which have not been summarized so far. The importance of locally synthesized complement will receive special emphasis, as several immunological processes take place in tissues, where hepatocyte-derived complement components might not be available at high concentrations. We also aim to call the attention to important differences between human and mouse systems regarding C3-mediated processes.

Role of complement 3a in the growth of mesangial cells from stroke-prone spontaneously hypertensive rats

Vascular smooth muscle cells (VSMCs) derived from spontaneously hypertensive rats (SHR) show exaggerated growth with a synthetic phenotype and angiotensin II (Ang II) production associated with increased production of complement (C3). We hypothesized that C3 is involved in the growth of mesangial cells (MCs) from hypertensive rats. We examined the effects of a C3a receptor inhibitor on proliferation, phenotype and Ang II generation in MCs from stroke prone-spontaneously hypertensive rats (SHR)-SP, SHR and Wistar-Kyoto (WKY) rats. Expression of C3 and C3a receptor were evaluated by immunohistochemical staining of the renal cortex. We examined the effects of the C3a inhibitor, SB290157, on proliferation, the expression of phenotype-marker mRNAs and Ang II production in cells from SHR-SP, SHR and WKY rats. Immunostaining of C3 was stronger in SHR and SHRSP glomeruli. MCs from SHR-SP and SHR abundantly express pre-pro C3 mRNA. SB290157 significantly inhibited basal DNA synthesis and proliferation of MCs from SHR-SP and SHR. Expression of osteopontin mRNA in MCs from SHR-SP and SHR was decreased with SB290157 treatment, whereas MC basal expression of α-SMA mRNA was decreased. SB290157 significantly decreased the production of Ang II in MCs from SHR-SP and SHR. Endogenous C3a promotes exaggerated growth with a synthetic phenotype and the production of Ang II in MCs from SHR-SP and SHR. The C3 and C3a receptor system may primarily be involved in the pathogenesis of renal remodeling in hypertensive rats.

Role of complement 3a in the synthetic phenotype and angiotensin II-production in vascular smooth muscle cells from spontaneously hypertensive rats

Background

Spontaneously hypertensive rats (SHR)-derived vascular smooth muscle cells (VSMCs) show exaggerated growth with a synthetic phenotype and angiotensin II (Ang II)-production. To evaluate the contribution of complement 3 (C3) or C3a toward these abnormalities in SHR, we examined effects of a C3a receptor inhibitor on proliferation, phenotype, and Ang II-production in VSMCs from SHR and Wistar–Kyoto (WKY) rats.

Methods

Expression of pre-pro-C3 messenger RNA (mRNA) and C3 protein was evaluated by reverse transcription-PCR and western blot analyses, and C3a receptor mRNA was evaluated by reverse transcription-PCR analysis in quiescent VSMCs from SHR and WKY rats. We examined the effects of the C3a inhibitor, SB290157, on proliferation and the expression of phenotype-marker and Krueppel-like factor 5 (KLF-5) mRNAs in VSMCs from SHR and WKY rats. We examined effects of C3a receptor inhibitor, SB290157, on Ang II-production in conditioned medium of VSMCs from SHR and WKY rats by a radioimmunoassay.

Results

Expression of pre-pro-C3 mRNA and C3 protein was significantly higher in SHR VSMCs than WKY VSMCs. SB290157 significantly inhibited proliferation of VSMCs from SHR, but not in cells from WKY rats. Relative to WKY VSMCs, SB290157 significantly increased the low expression of SM22α mRNA and decreased the high expression of osteopontin mRNA in SHR VSMCs. SB290157 significantly decreased the high expression of KLF-5 and Ang II-production in VSMCs from SHR, but not in cells from WKY rats.

Conclusions

C3a induces exaggerated growth, a synthetic phenotype and Ang II-production in SHR-derived VSMCs. C3a may be primarily involved in cardiovascular remodeling in hypertension.

A novel, complement-mediated way to enhance the interplay between macrophages, dendritic cells and T lymphocytes

Recently it has been reported that human C3-deficiency is associated with impairments in dendritic cell differentiation. Here we investigated how complement C3 influences the phenotype and functional activity of human dendritic cells. We show that human monocyte-derived dendritic cells (MDCs) when incubated with native, hemolytically active C3, bind the activation fragments of C3 covalently. This reaction directs MDCs to increase expression of MHCII, CD83 and CD86, moreover it results in a significantly enhanced secretion of TNF-alpha, IL-6 and IL-8. A further functional consequence of C3b-fixation is the elevated capacity of the dendritic cells to stimulate allogeneic T cells. The distinct role of covalently fixed C3-fragments is strongly supported by our results obtained with MDCs where CD11b expression was downregulated by siRNA. To reveal the possible in vivo significance of the present findings we modelled a phenomenon occurring during inflammation, where C3 is produced locally by activated macrophages. In these cocultures MDCs were found to fix substantial amounts of macrophage derived C3-fragments on their cell membrane. Our data provide compelling evidence that antigen presenting cells arising in complement-sufficient environment mature to competent stimulators of T cells.

Complement 3 is involved in changing the phenotype of human glomerular mesangial cells

Complement activation contributes to tissue injury in various forms of glomerulopathy and is characterized by deposition of complement components, which accelerates the progression of chronic renal damage. We recently reported that complement 3 (C3), a critical component of the complement system, is associated with the synthetic phenotype of vascular smooth muscle cells. It is possible that C3 stimulates mesangial cells to assume the synthetic phenotype to, in turn, induce glomerular injury and sclerosis. We investigated the role of C3 in the growth and phenotype of mesangial cells. Cultured human mesangial cells (HMCs) expressed C3 mRNA and protein, and levels were increased in response to IFN-gamma and TNF-alpha. HMCs also expressed C3a receptor mRNA and protein. Exogenous C3a stimulated DNA synthesis in HMCs in a dose-dependent manner. C3a decreased expression h-caldesmon mRNA, a marker of the contractile phenotype, and increased the expression of osteopontin, matrix Gla, and collagen type1 alpha1 (collagen IV) mRNAs, which are markers of the synthetic phenotype. C3a decreased expression of alpha-smooth muscle actin in HMCs. Small interfering RNA (siRNA) targeting C3 reduced the DNA synthesis and proliferation of HMCs, increased expression of h-caldesmon mRNA, and decreased expression of osteopontin, matrix Gla, and collagen IV mRNAs in HMCs. These results indicate that C3 causes HMCs to convert to the synthetic phenotype and stimulates growth of mesangial cells, suggesting that C3 may play an important role in phenotypic regulation of mesangial cells in renal diseases.

C3-induced 3LL cell proliferation is mediated by C kinase

It has been demonstrated that the third component of complement (C3)(1) and its peptides increase normal and tumour cell proliferation. However, the signal cascade responsible for this phenomenon is still unknown. In this study, we elucidate some of the mechanisms involved in the signalling of C3 stimulation of cell proliferation. We have first investigated the in and out traffic of C3 peptides, then we have identified the subcellular localisation of internalised C3 and, finally, we have explored the role of protein phosphorylation in C3 traffic and in the proliferation of the Lewis lung carcinoma (3LL) cells. Our results indicate that traffic of C3 is not dependent on cytoskeletal integrity and requires protein kinase C-dependent phosphorylation. In addition, proliferation of 3LL cells stimulated by C3 depends on both C3 internalisation and protein-kinase C phosphorylation.

Complement 3 is involved in the synthetic phenotype and exaggerated growth of vascular smooth muscle cells from spontaneously hypertensive rats

Vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) show the synthetic phenotype and exaggerated growth in comparison with VSMCs from normotensive Wistar-Kyoto (WKY) rats. We investigated genes associated with the synthetic phenotype and exaggerated growth of VSMCs from SHR by microarray. Expression of 1300 transcripts was evaluated by microarray with total mRNA extracted from mid-layer aortic smooth muscle of 3-week-old SHR/Izumo and WKY/Izumo rats. mRNAs encoding sodium-dependent neurotransmitter transporter, epidermal growth factor precursor, EEF2, leptin receptor long-isoform b, clathrin assembly protein short form, and preprocomplement 3 (pre-pro-C3) were expressed only in aortic smooth muscle from SHR by microarray and by reverse-transcription polymerase chain reaction analysis. Pre-pro-C3 mRNA was detected only in cultured VSMCs from SHR. Exogenous C3 changed VSMCs to the synthetic phenotype. Antisense oligodeoxynucleotides (ODN) to C3 reduced the higher level of DNA synthesis in VSMCs from SHR. Antisense ODN to C3 increased expression of SM22alpha mRNA and decreased expression of osteopontin and matrix Gla mRNAs. It also decreased expression of growth factor mRNAs in VSMCs from SHR. In conclusion, we have shown that C3, independent of other complement molecules, has direct effects on the phenotype of VSMCs and stimulates growth of these cells. C3 is produced only by VSMCs from SHR. Therefore, C3 may be the gene underlying the synthetic phenotype and exaggerated growth of VSMCs from SHR. C3 may be a new target for the treatment of hypertension.

C3 synthesis and CRs expression during differentiation of a murine stem cell line

C3 production, release and CRs expression during the neutrophilic differentiation of a murine non tumorigenic cell line is investigated. The murine non tumorigenic cell line 32DCl3(G) which undergoes terminal differentiation into polymorphonuclear granulocytes when cultured in presence of G-CSF was selected as a suitable in vitro model for this study. The results show that as the cells progress into the differentiation program, levels of C3 mRNA increase, accompanied by increased C3 production. As differentiation progresses the cells gradually express CRs on their surface; these are undetectable on the surface of undifferentiated cells. As a consequence of CRs appearance, cells become able to bind C3 through receptorial binding. Differences were found in the modality of C3 secretion: differentiated cells tend to store C3 in their intracellular compartments rather than secrete it continuously into the medium and they respond to membrane stimulation with increased secretion of C3. Treatment of 32DCl3(G) with TNF-alpha increased C3 production in a time- and dose-dependent fashion. Cell response to this stimulus progressively increases during the differentiation process suggesting that they acquire functionality in the signal transduction mechanisms.